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Author Topic: Softening hard carb boots  (Read 42148 times)

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Offline lucky

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Re: Softening hard carb boots
« Reply #75 on: April 04, 2012, 10:38:56 am »
Hi, everyone.
This is Pavel from NY.
I recently got my first bike(a small project) 1978 cb750k (k8)
And lo and behold... I learn about the imposibility to get the 2 and 4 carb insulators(boots).
So, not giving up I ordered two new sets of 1 and 3.
Took the old cracked, broken rocks of carb boots off and put the correct new ones in.
Then the fun began - the 2 and 4, although exact mirror images of 3 and 1, are not interchabgable - due to the vertical incline of the intake openings (so they are tilted both horizontally to reach the wider carbs; and vertically for no apparent reason other then improved mixture flow).

When flipped around the engine side of the boot points up and to the right.... ugh
Anywho, I didnt give up then either - I flipped all four boots ever so slightly to come closest possible to a flat and even fit with the carbs. Put everything together and there was improvement, but no way of telling wether I got sufficient sealing.

Can you guys recommend a way to tell if I am losing vacuum at the boots before I look into carb tuning?

Oh, and of course, I am looking for new boots 16112-405-000 and 16114-405-000 or home made versions. I'll take pics when I take carbs off again to show what I am on about for others in my shoes.
If you haven't figured it out already, you want to spray the boots at idle with some starter fluid.  You want to listen for a change in RPM as your spraying.  If you have a leak, the starter fluid being sucked in will compensate for a lean mix(to much air).  I am going through the same bs with my K8, I've been looking for new boots, or nice used boots for months...damn bike, it's always something with this thing.  I may just try the wintergreen treatment, don't have a choice at this point if I want to ride my bike again this year.

Remember you are looking for a used 33 year old part. There are probably no "good" ones.


Offline Celco

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Re: Softening hard carb boots
« Reply #76 on: April 04, 2012, 08:59:02 pm »
I was searching high and low for wintergreen oil locally the past few days and only finding it for $14 an oz.  While I was tinkering in the garage I noticed something.  Marvel Mystery Oil smells good... and what do you know, its got (im sure in small amounts) wintergreen oil in it.  Now I don't know what sparked people to try soaking in ATF and other oils, but would some MMO and Xylene maybe work out instead of trying to track down ridiculously expensive specialty oils?

Offline jukku

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Re: Softening hard carb boots
« Reply #77 on: May 18, 2012, 12:41:47 pm »
Diy carb boots is working well on a CB750A Hondamatic. Almost impossible to find stock carb boots.
Have been tested one summer, almost 5000 miles. Diy boots are better than cracked stock boots.


32 mm Silicone hose as carb boots. Very easy to cut if you have the carbs and a cylinderhead on your workbench! Not a perfect match but good enough until you get original  boots ;)
« Last Edit: May 18, 2012, 12:45:00 pm by jukku »

Offline HondaMan

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Re: Softening hard carb boots
« Reply #78 on: May 18, 2012, 09:44:49 pm »
I was searching high and low for wintergreen oil locally the past few days and only finding it for $14 an oz.  While I was tinkering in the garage I noticed something.  Marvel Mystery Oil smells good... and what do you know, its got (im sure in small amounts) wintergreen oil in it.  Now I don't know what sparked people to try soaking in ATF and other oils, but would some MMO and Xylene maybe work out instead of trying to track down ridiculously expensive specialty oils?

My long-term experience is: if you soak them in just xylene (about 2-3 days), they get soft and swell up, then after about 3-4 days they shrink back down. In one case, I installed them on the bike while swelled (they would barely stay on, so big!), and they sort of shrank-to-fit over the next week, very tight now. The ones that I have added wintergreen oil to have swelled a little less, but also stayed at the size and stayed soft, while the xylene-only ones are hard again. They don't seem to leak, just got hard.
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

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Offline spivey

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Re: Softening hard carb boots
« Reply #79 on: February 22, 2018, 06:35:53 pm »
I know this is a reaaaally old thread but I'm getting ready to give it a try on the rock hard intake boots on my '78 750. Any changes to the 50/50 xyzol/wintergreen oil mix? Any change to the week long soak? Is there anything you'd change or do differently. Finally how has the softness held up.
Thanks

Offline dave500

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Re: Softening hard carb boots
« Reply #80 on: February 23, 2018, 12:04:53 am »
if you re -fitting them I boil em in water,then work quick with a little oil or rubber grease,they plop straight on but still need a little muscle.

 

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